1. Field of the Invention
The present invention relates to the structure of a throttle valve for a control valve device which adjusts the amount of intake air for an internal combustion engine.
2. Discussion of Background
In FIG. 6, there is shown a conventional control valve device which adjusts the amount of intake air for an internal combustion engine, and which is depicted as a plan view in FIG. 6(a) and as a vertical sectional view in FIG. 6(b), and has a portion in the vicinity of a throttle body wall 1 and a peripheral portion of a throttle valve 2 depicted as an enlarged view in FIG. 6(c). In the control valve device, an intake air passage 4 is formed for air flow. The throttle body wall 1 which has the intake air passage 4 formed therein has a throttle valve shaft 3 rotatably carried thereon. The throttle valve 2, which is formed in a plate-like shape, is fixed on the throttle valve shaft 3 so as to be freely rotatable. The throttle valve 2 is rotated by the throttle valve shaft 3 operated by an acceleration pedal to provide a mechanism for adjusting the amount of intake air for the internal combustion engine.
In the control valve device, air, the amount of which is regulated by the position of the throttle valve 2, is mixed with fuel when operating the engine, and the mixture is forwarded into the engine. At that time, an exhaust gas or a blow-by gas including carbon and oil sometimes flows toward the side of the throttle valve 2 from the side of the engine. When the throttle valve 2 is nearly shut or the gap between the throttle valve and the throttle valve wall 1 is small, an outer peripheral portion of the throttle valve 2 which confronts the throttle body wall 1 has the carbon or oil deposited thereon. It can be solidified to prevent the throttle valve 2 from properly.
In particular, the latest trend in internal combustion engines is to decrease the setting angle of the throttle valve 2 for idling in order to lower the idling spend. Such decrease in the setting angle of the throttle valve for idling introduces easy adherence of the deposit such as carbon or oil on the outer peripheral portion of the throttle valve. The deposit is solidified by e.g. heat from the internal combustion engine to become a solid deposit 5. Further, additional oil or carbon is liable to adhere on the solid deposit 5, accelerating of deposition of the solid deposit 5.
As stated, when the intake air reflows into the control valve device from the internal combustion engine, the deposit such as carbon in the exhaust gas or oil in the blow-by gas adheres and is deposited on the outer peripheral portion of the throttle valve 2, and is solidified thereon. Such a state causes malfunction in the control valve device. In order to avoid such a state, there has been proposed e.g. a solution which is disclosed in JP-B-7-42870.
In FIG. 7, there is shown the control valve device disclosed in JP-B-7-42870. As shown in FIGS. 7(c) and (d), the throttle valve 2 is constituted by a thicker portion 2A at which the throttle valve is fixed on the throttle valve shaft 3, and a thinner portion 2B or 2C at the outer peripheral portion of the throttle valve 2. The thinner portion is formed to be stepwise thinner than the thicker portion 2A. In detail, the thickness of at least the outer peripheral portion of the throttle valve 2 becomes stepwise thinner to decrease the thickness of the portion of the throttle valve 2 confronting the throttle body wall 1 so as to lower the adherence amount of the deposit on that portion, allowing the malfunction in the throttle valve 2 to be prevented.
The conventional control valve device for adjusting the amount of intake air for an internal combustion engine, generally, has the throttle valve formed to have a constant thickness as shown in FIG. 6. When the intake air reflows into the control valve device from the engine, the deposit such as carbon in the exhaust gas or oil in the blow-by gas adheres and is deposited on the outer peripheral portion of the throttle valve 2, and is solidified thereon. In order to cope with this problem, forming the throttle valve so as to be stepwise thinner as shown in FIG. 7 has been proposed by JP-B-7-42870. However, when the throttle valve 2 is formed to be stepwise thinned, the presence of the discontinuous stepwise shape of the throttle valve causes the deposit to accumulate at a stepped corner easily and the flow of air passing through the intake passage 4 to be unstable, contributing e.g. wind noise.